Biomolecules and Chemistry in Everyday Life 1 Question 14
16. The predominant form of histamine present in human blood is $\left(\mathrm{p} K_{a}\right.$, Histidine $\left.=6.0\right)$
(2018 Main) (a)
(c)
(b)
(d)
Show Answer
Solution:
- Our blood is slightly basic in nature with $\mathrm{pH}$ range from 7.35-7.4. The structure of histamine is given below :
Aliphatic
Basic nitrogen of imidazole ring
It is produced by decarboxylation of histidine having following structure. It is clearly visible from the above structure that histamine has two basic centres namely aliphatic amino group and basic nitrogen of imidazole ring. The aliphatic amino group has $\mathrm{p} K_{a}$ around 9.4. In blood with $\mathrm{pH}$ around 7.4 the aliphatic amino group of histamine become protonated to give a single charged cation as shown below
